Analysis of quality of life (QOL) has revealed that preservation of swallowing, speech, and breathing functions has a direct impact on QOL and that these functions are important patient-reported outcomes. The purposes of this study were to adapt and culturally validate the M.D. Anderson Dysphagia Inventory (MDADI) to the Brazilian Portuguese language and to evaluate QOL related to dysphagia in patients treated for head and neck cancer. This was a cross-sectional study that included 72 adult patients with a mean age of 63 years who were treated for head and neck cancer. Construct validity and reliability analyses were performed through the comparison of the MDADI with three other health-related QOL questionnaires administered at the time of enrollment and MDADI application 2 weeks thereafter, respectively. Reliability was established by assuring both internal consistency (Cronbach’s α) and test–retest reliability (intraclass correlation coefficient, ICC). Test–retest reliability for the total score in the MDADI had an ICC greater than 0.795 (p < 0.001). The MDADI had significant statistical correlations with the other questionnaires. Patients treated for head and neck cancer had a mean total score of 83 on the MDADI, which is indicative of minimal limitation in overall QOL. In conclusion, the present study validates the adaptation of the MDADI to the Brazilian Portuguese language and provides another tool to evaluate the impact of dysphagia on the QOL of head and neck cancer patients.